Three new isocoumarin derivatives, tabaisocoumarins A-C (1-3), together with three known phenolic compounds (4-6), were isolated from the roots and stems of Nicotiana tabacum. Their structures were elucidated by spectroscopic methods, including extensive 1D- and 2D NMR techniques. Compounds 1-6 were evaluated for their anti-tobacco mosaic virus (anti-TMV) activities at the concentration of 20 mu M. Compound 2 exhibited anti-TMV activity with inhibition rate of 33.8%, which is higher than that of positive control, ningnanmycin. The other compounds also showed potential anti-TMV activities with inhibition rates in the range of 18.7-28.5%, respectively. (C) 2014 Published by Elsevier B.V. on behalf of Phytochemical Society of Europe.